Project Summary/Abstract Pediatric brain trauma is a significant debilitating health problem among children in the United States. To date, there is no effective treatment to structurally repair the injured brain and restore the lost neurological functions associated with brain trauma. Cell transplantation offers hope to treat the injured brain through direct neural replacement to replenish cells lost to injury and reconstruct the disrupted neuronal circuitry or/and by stimulating endogenous repair mechanisms. However, current approaches have encountered prominent issues such as ethical controversies of cell source, limited cell availability, poor graft survival, lack of functional integration of grafted cells, the risk of tumor formation and immunological rejection. Recent advances in tissue engineering and induced pluripotent stem cells (iPSCs) have instilled new hope to develop patient-specific autologous cell source to overcome the issues that neural transplantation has encountered. Utilizing iPSCs and our well-constructed injectable hydrogel system, the goal of this proposal is to develop a biomaterial- assisted cell transplantation strategy through modulating the host microenvironment to enhance brain structure remodeling and improve survival, neuronal differentiation and functional integration of grafted cells achieving repair and regeneration of the injured pediatric brain following traumatic injury. We have previously developed a series of injectable in-situ cross-linkable hydrogels to promote the reconstruction of a complete vascular network in the injured adult brain. We have also optimized our hydrogel system for supporting three dimensional growths of cells and as a delivery vehicle releasing bioactive reagents. In this proposal, we plan to utilize our hydrogel system to modify the host environment to promote long term survival, neuronal differentiation and functional integration of the transplanted iPSC-derived neural stem cells (iPSC-NPs) in the injured pediatric brain via reconstruction of a complete vasculature network and conditioning of focal tissue microenvironment at the site of injury. We will test the central hypothesis that a combination of iPSCs transplantation with targeted tissue bioengineering will achieve optimal brain tissue regeneration and enhance functional recovery following pediatric brain injury. The hypothesis will be tests in two Specific Aims, 1) Optimize the biomechanical and biochemical properties of our injectable hydrogel system to promote the growth of primary neurons, endothelial cells isolated from neonatal brain and iPSC-NPs in vitro, 2) Utilize injectable hydrogels optimized for neonatal brain cell growth to reconstruct local vasculature and deliver growth promoting molecules in combination with iPSC-NPs to promote tissue structural regeneration and functional recovery following pediatric brain injury. The results of this study will advance the understanding of the key microenvironmental requirements for successful neural transplantation therapy and will have translational significance not only for TBI but also for other neurological diseases.